Luminescent germanates



' Dec. 26, 1961 H. KOELMANS ETAL 3,

LUMINESCENT GERMANATES Filed March 17, 1960 250 300 350 1.00 A 450m,u

IN ENTORS HEIN KOE LM ANS CATHARINA M.C.VE RHAGEN BY z ,4 xf.

AGEN

Unite States Patented Dec. 26, 1961 ice This invention relates to new and novel luminescent substances.

More particularly this invention relates to new and novel luminescent materials having their maximum output efiiciencies within the long ultraviolet region.

It is a principal object of this invention to prepare new and novel luminescent substances which exhibit high quantum efliciencies between 300 m and 400 mu.

According to the invention new and novel luminescent germanates are prepared. These new and novel germanates satisfy the formula 2MO.1QO.2GeO :XPb wherein M represents at least one element selected from the group consisting of barium and strontium, Q represents at least one element selected from the group consisting of zinc and magnesium and x has a value between 10 and l- The germanates of the invention have a conversion efficiency that is substantially equal to that of the cor responding silicates. However, upon excitation with radiation of 253.7 m the germanates exhibit maximum emissions at longer wavelengths more particularly between 325 me and 385 Ill/L. Because the maximum emissions occur in this range the germauates of the invention are particularly suitable for use as the ultraviolet source in radiation sources used in blueprinting and in causing advertising signs coated with luminescent paint to light up.

The compounds in accordance with the present invention containing only barium have an emission maximum at a slightly longer wavelength than the corresponding compounds containing only strontium. For mixed compounds, the emission maximum lies between. The proportion of lead in the range of the invention only slightly influences the position of the emission maximum. However, outside the above-mentioned range of the lead concentration, the intensity of the emission is too small for practical use. The elements zinc and magnesium are equivalent with respect to the position of the emission maximum.

The invention will now be described more fully with reference to a number of examples of preparing various germanates in accordance with the invention and the accompanying drawing. The sole figure in the drawing is a graph in which the wavelengths in me are plotted as abscissae and the relative intensities of the emitted radiation are plotted as the ordinates. For each curve, the maximum has been converted to 100 in order to allow a satisfactory comparison of the positions and shapes of the emission curves. All the curves are made with excitation by a radiation having a wavelength of 253.7 run.

In the examples that follow the initial composition of the mixture always is such that it is substantially precluded that the final product still contains any germanium dioxide since the germanium dioxide exhibits a large ultraviolet absorption.

Example 1 77 g. of BaCO 8 g. of MgO 0.7 g. of MgF 42 g. of'GeO are thoroughly mixed. 40 ml. of a 0.1 N-solution of Pb(NO are added to the mixture. After drying the paste, the substance is heated in air to 1100 C. for 2 hours. The fired product shows an intense ultraviolet emission on excitation by a radiation source having a wavelength of 253.7 me. The emission curve is designated 1 in the drawing. The quantum eificien'cy of the resultant luminescent substance is approximately Example 2 57 g. of SrCO 15 g. of ZnO 1 g. of ZnF 42 g. of GeO are thoroughly mixed. ml. of a 0.1 N-solution of Pb(NO are added to the mixture. After drying the paste, the substance is heated in air to 1050 C. for 2 hours. After cooling the product is ground and then again heated in air to 1100 C. for 2 hours. The final product shows a comparatively intense ultraviolet emission on excitation by a radiation source having a wavelength of 253.7 mg. The emission curve is designated 2 in the drawing. The quantum efliciency of the resultant product is approximately 40%.

Example 3 39 g. of BaCO 29 g. of SrCO 8 g. of MgO 0.7 g. of MgF 42 g. of Ge0 are thoroughly mixed. 10 ml. of a 0.1 N-solution of Pb(NO are added to the mixture. After drying the moist mixture, it is heated in air to a temperature of 1100 C for 1 hour. After cooling, the fired product is ground and then again fired at 1150 C. for 2 hours. The final product shows an intense ultraviolet emission on excitation by a radiation source having a wavelength of 253.7 m The emission curve is designated 3 in the drawing. The quantum efiiciency of the resultant product is approximately 80%.

Example 4 59 g. of SrCO 7 g. of 2110 1 g. of ZnF 4 g. of MgO 42 g. of GeO are thoroughly mixed. 200 ml. of 0.1 N-solution of Pb(NO are added to this mixture. After drying, the mixture is heated in air to a temperature of 1050 C. for 1 hour. After cooling, the fired product is ground and then again heated to a temperature of 1150 C. in air for 2 hours. The final product shows an intense ultraviolet emission on excitation by a radiation source having a wavelength of 253.7 m The emission curve of the prodnot substantially coincides with the curve 3 of the drawing. The quantum efiiciency of the obtained product is approximately 45%.

In the above examples, the fluorides of magnesium or Zinc are used as fluxes. This results in an improved crystallization state of the final products, which state can be obtained at a lower temperature than without a flux. Obviously, the amount of zinc or magnesium introduced by the flux into the final product is allowed for.

While we have described our invention in connection with specific embodiments and applications, other modiiications thereof will be readily apparent to those skilled in this art without departing from the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

l. Luminescent materials corresponding to the general formula:

wherein M represents at least one element selected from wherein Q represents at least one element selected from the group consisting of Zinc and magnesium and X has a value between 10 and 10' 3. Luminescent materials corresponding to the general formula:

2SrO.1QO.2GeO :XPb

wherein Q represents at least one element selected from the group consisting of zinc and magnesium and X has a value between HIV and 10- 4. Luminescent materials corresponding to the general formula:

2MO.1ZnO.2GeO :XPb

wherein M represents at least one element selected from the group consisting of barium and strontium, and X has a value between 10* and 1O 5. Luminescent materials corresponding to the general formula:

2MO.1MgO.2GeO :XPb

wherein M represents at least one element selected from the group consisting of barium and strontium, and X has a value between 1() and 10" References (Iiteai in the file of this patent UNITED STATES PATENTS 2,457,054 Leverenz Dec. 21, 1948 OTHER REFERENCES Koelmans et al.: The Fluorescence of Binary and Ternary Gennanates of Group II Elements, Journal of the Electrochemical Society, August 1959, pages 677-681. 

1. LUMINESCENT MATERIALS CORRESPONDING TO THE GENERAL FORMULA: 